1. Field of the Invention
This invention relates to leads, or catheters, adapted for insertion into a patient's heart for transmitting signals between the heart and a device such as a pacer, and more particularly a lead adapted for atrial insertion.
2. Description of the Prior Art
In the field of electronic cardiac pacing, there is a certain utilization of pacers designed to provide stimulus pulses to the patient's atrium or receive signals from the atrium, or both. As with ventricular pacing, it is desirable, if possible, to introduce the catheter or lead transvenously through the superior vena cava. For placement of a lead tip within the ventricle, little difficulty is encountered since the lead can simply be inserted until the tip reaches the apex of the right ventricle. However, the procedure is not quite so simple or so reliable with respect to the atrium, due to the dimensions of the atrium. The atrium has no apex corresponding to the ventricle, and a lead which is simply inserted to the point where the tip is within the atrium would not attain fixation in most cases, since it would be more or less suspended within the atrium. In order to overcome this difficulty, the procedure adopted most generally in the prior art is to introduce a J-shaped or other type of curvilinear electrode which enables the tip to be forced into contact with the inner atrial wall. Examples of such electrodes are seen in many U.S. Pats., including Nos. 3,729,008; 3,865,118; 3,949,757; and 4,057,067.
A common form of atrial lead found in the prior art is a lead having a preset curve at the end of the lead, or the end of the atrial component of the lead in the case of leads designed to have both atrial and ventricular tips. In order to be able to introduce the lead transvenously, the preset curved portion is maintained in a straight form by a stylet while the lead is being introduced into the patient's body. Upon having positioned the lead within the atrium, the stylet is withdrawn, permitting the atrial tip to assume the preset curvilinear form. However, with such a lead the physician who is introducing the lead has relatively little capability for positioning the tip after the stylet has been withdrawn. Rotation of the lead about its axis causes the entire curvilinear tip portion to rotate or flop around relative to the lead axis just preceding the curved portion; it is not possible, with this type of lead, to simply rotate the distal end where the electrode tip is located while holding the axial configuration fixed.
In the U.S. Pat. to Babotai, No. 4,026,303, issued May 31, 1977 and assigned to the same assignee as this application, there is disclosed an endocardial electrode having a closed helical tip which is particularly well adapted for engaging the trabeculae on the inner lining of the heart wall. This type of tip is adaptable for use in an atrial lead as well as a ventricular lead. In utilizing the electrode as shown in the Babotai patent, it is necessary for the physician to rotate the proximal end of the electrode, thereby imparting rotation to the distal tip, the rotation enabling the proper positioning of the tip so that the trabeculae can enter and engage the open grooves of the closed helix. However, this sort of closed helical tip can not be utilized with the prior art type of atrial lead since rotation of the proximal end of the lead would cause the entire curvilinear portion at the distal end to flop around, such that the helical tip could not be rotated into fixation with the trabeculae. There is thus a need for a lead assembly which enables the physician to insert the lead transvenously until the atrial tip portion has reached the atrium, to then introduce a curvilinear form to the atrial tip so that it comes into engagement with the atrial wall, and to then rotate the atrial tip about its axis while such axis is maintained substantially fixed, so that the tip can be brought into optimal engagement and fixation with the atrial trabeculae.